A database management system is accessed and managed through sessions “requests.” A request can be a query, through which the database is accessed, or an instruction to execute a utility, such as a load command. Most database management systems use an optimizer to select an access plan, or query execution plan, for a database request and most optimizers rely on a cost model, where cost is associated with the amount of a resource, such as CPU or I/O, that must be devoted to a task, to choose the best access plan to execute any given request. Most cost models rely on a mathematical construct that uses estimates of the numbers of rows (cardinalities) which will result at each step of the access plan. The estimates are often based on assumptions regarding the contents of the database tables.